Horizontal directional drilling is a method of installing underground pipelines. The drill head has the ability to turn and follow a curved path, thus allowing a horizontal bore to be made. The drill head continues in a straight path until it is turned upwards to the surface at a desired point. A pipeline is then pulled into and through the bore made by the drill head. This method of installing underground pipelines has become very popular because it has the advantage of not requiring an open-cut trench to be dug.
A major difficulty with horizontal directional drilling arises when installing the pipeline. As the pipeline is pulled into and through the bore, regular PVC pipes, which are connected by gasketed, push-on joints, tend to become separated due to axial forces which result from the pipeline being pulled through the bore.
The standard solution for preventing PVC pipes from becoming separated has been to use high density polyethylene or steel joints that are fusion welded together. However, welding is not a preferred process as the labour involved is relatively expensive. Furthermore, fusion welded joints are difficult to replace.
Other solutions include bell and spigot type joints wherein the spigot end of one pipe is inserted into the bell end of a second pipe and corresponding features on the bell and spigot ends interact to prevent the two pipes from separating. For example, U.S. Pat. No. 3,701,548 (McGuire) discloses a system for joining plastic pipes using a bell and spigot type joint. The bell portion of a first pipe end has a plurality of longitudinal passages circumferentially spaced therearound. A circumferential passage extends from one side of each longitudinal passage on the bell portion. The spigot portion of a second pipe end includes a plurality of lugs circumferentially spaced around and extending radially outward, which lugs are received in the longitudinal passages of the bell portion. The circumferential passages are positioned and shaped to draw a mating end of the spigot portion into a firm seating engagement with a seat within the bell portion upon relative rotation of the bell and spigot portions to move the lugs along the respective circumferential passages.
U.S. Pat. No. 3,813,115 (French) teaches a bell and spigot type joint for plastic pipes. The spigot end includes a continuous helical rib integrally formed with and protruding out from its external surface. The bell end includes a continuous helical groove formed integrally around its internal surface. The helical groove of the bell end receives the helical rib of the spigot end in a threaded fashion.
U.S. Pat. No. 5,662,360 (Guzowski) discloses an interlocking restraint plastic pipe joining system which includes pairs of female and male integral end connections. The female end connection has at least one depression within a mouth opening thereof. The male end connection has at least one protrusion formed on an exterior surface thereof which is adapted to matingly engage, in a snap fit fashion, the depression in the mouth opening of the female member.
Other solutions also include bell and spigot type joints which utilize bolts as fastening mechanisms. For example, U.S. Pat. No. 4,296,953 (Nago et al.) teaches a pipe joint for preventing a spigot from slipping off from a socket. The spigot and socket are provided with engaging members which are engageable with each other axially thereof. In one embodiment, headed bolts are inserted into the socket from outside through a hole in the socket wall and screwed into a threaded bore.
U.S. Pat. No. 4,318,639 (Schosek) discloses a plastic pipe connector fitting. In addition to using a threaded joint, Schosek discloses the use of lock bolts which are threaded through radially aligned threaded holes in the pipe sleeves. The inner end of each lock bolt is provided with a peripheral cutting edge and therefore, the ends of the plastic pipe need be pre-drilled.